1. Field of the Invention
This invention is directed to antenna arrays, in general, and to a planar antenna array which is capable of operating on a plurality of different frequency bands with superior operating characteristics, in particular.
2. Prior Art
There are many types of antennas and arrays which are known in the art. These antennae include many structural configurations. Within the context of the instant invention, the most pertinent antenna arrays which are known in the art are, typically, the parabolic dish antenna array and a planar antenna array. In the environment and configuration contemplated herein, these antennae have the dimensions of approximately six to seven feet in diameter (for the parabolic dish) and about seven feet square (for the planar array). In the known antennae configuration, each antenna is usually arranged to be tuned to operate upon (i.e. transmit or receive) a single frequency. This is usually achieved by placing the transmitter or radiating element (in a parabolic dish unit) at the center or focal point of the dish antenna. In this case, a high degree of accuracy and a very small degree of tolerance is permitted in producing the device.
Conversely, in the planar array which is known in the art, all of the radiating elements in the array are of substantially the same size and configuration in order to achieve an accurate signal configuration.
In an attempt to provide additional operational capability, some known parabolic and/or planar arrays utilize additional elements which are slightly modified so as to provide additional frequency capabilities. However, in the known planar arrays, the radiating elements are designed to produce frequencies which are within the same band, i.e. C, X or Ku. In the parabolic dish arrangement, the additional frequency capability is achieved by using two radiating elements which are slightly off the focal point of the dish and placed on some other compromise arrangement. Obviously, this produces a less than ideal apparatus without significantly improving the apparatus itself or its operation.
For a description of one type of planar array antenna, reference is made to the IEEE Transactions On Antennas And Propagation, Vol. AP29, No. 1, January 1981, pages 25-37, entitled "MICROSTRIP ARRAY TECHNOLOGY" by R. J. Mailloux, et al.
Another reference is an article by K. C. Gupta entitled "RECENT ADVANCES IN MICROSTRIP ANTENNAS", which appeared in the "Microwave Journal" October 1984 issue on pages 50-66.